In general, there is a known outside-type filtering apparatus for filtering water in a aquarium to purify it in order to breed and rear aquarium fishes such as goldfishes, tropical fishes and the like in the aquarium, which includes a filter device which is externally hitched and supported on a wall surface of the aquarium, and a water pump which is connected to the filter device, so that water in the aquarium is forcibly circulated through the filter device where it is filtered, and the filtered water is returned into the aquarium (for example, see the specification of U.S. Pat. No. 4,512,885).
It should be noted here that in such outside-type filtering apparatus, the filter device which is a main member of the apparatus can be mounted outside the aquarium. Therefore, the outside-type filtering apparatus is generally and widely utilized, because there are advantages that the filtering apparatus cannot reduce an effective volume within the aquarium and moreover, cannot deteriorate the sight within the aquarium, and that the maintenance such as the exchange of parts of the filtering apparatus and the cleaning of the filtering apparatus is easy.
In the conventionally known outside-type filtering apparatus, however, the water pumped into the aquarium by the water pump is pressurized and fed into the filter device by the water pump, and the total amount of the water is passed through the filter element for filtration.
In the conventional filtering apparatus, however, because the pressurized water from the water pump is passed, as it is, through the filter element, whereby it is filtered, the following disadvantage is encountered: The water is difficult to flow equally over the entire region of the filter element (the water flows partially relative to the filtering surface), thereby bringing about a reduction in filtering efficiency and further causing the partial clogging of the filter element. Such disadvantage tends to be increased, as the filtering area of the filter element is increased.
Because the total amount of the pressurized water from the water pump is passed through the filter element, the following problem is also encountered: The flow speed of the water flowing through the filter element is too rapid, which is inappropriate for propagation of aerobic microorganisms required for the purification of the water in the filter element, thereby bringing about a further reduction in filtering efficiency in cooperation with the above-described disadvantage and problem to hasten the exchange and maintenance frequencies for the filter element.